1. Field of the Invention
This invention pertains generally to wireless communication, and more particularly to increasing wireless throughput by exploiting channel gain information beyond mere prediction.
2. Description of Related Art
Wireless communications has become ubiquitous in our modern world, with ever expanding capabilities to communicate between parties in motion, such as via cell phones. Numerous standards have been developed for communicating wirelessly at faster rates, more securely, and over a wider range of conditions (robustness).
The use of multiple transmitters and receivers (e.g., Multiple Input, Multiple Output (MIMO), Space-Division Multiple Access (SDMA)), provided gains in speed and security while being more robust.
Toward enhancing these multiple transmit, multiple receiver, communication systems, information about channel gains have been utilized for predicting current channel gains at the time of transmission. It will be noted that the data from the transmitting node to the receiving node is sent through a time-varying channel, one for each receiving node, whereby information about the time-varying gains of the channels is assumed to be available at the transmitting node, yet only after a certain delay. This delay may be caused by the need for the channel gains of a receiving node, also referred to as a Mobile Station (MS) to be measured at that receiving node and then fed back to the transmitter, also referred to as a Base Station (BS) through the uplink, or for some other reasons. Due to the delay and the time-variation of the channel gains, the current channel gains may be different from the delayed channel measurements.
Many state-of-the-art approaches for dealing with the delay when predicting channel gains try to exploit the time correlation of the channel to predict the current channel gains from the delayed measurements. The predicted channel gains are then utilized in a scheme such as multiuser transmit beamforming (also called downlink multiuser MIMO or SDMA, space-division multiple access) which can simultaneously send data to the multiple receiving nodes. This is also called spatial multiplexing.
However, as the time-variation of the channel becomes faster, due to higher mobility for example, the delayed channel information reveals very little information about the current channel gains, and a prediction-based scheme may offer negligible multiplexing benefits.
Accordingly, there is a need for methods, apparatus and systems which enhance throughput despite the problems associated with channel gain delays. The present invention fulfills this need and others, and overcomes the shortcomings of prior multiple transmit, multiple receive configurations.